The general benefits and value of conducting physical training in a hypoxic (oxygen-deprived or lower oxygen concentration than in normal air) environment are documented. For example, research in “Intermittent Hypoxic Training (IHT)” ranging from basic research (physiology, biochemistry, cell biology, etc.) to practical applications (athletic training, therapeutic applications) has been reported in a number of recognized, reputable journals appearing in the data base of the National Library of Medicine, including High Altitude Medicine and Biology; Anesthesiology; Chest, Bulletin of Experimental Biology and Medicine, Sports Medicine; International Journal of Sports Medicine; and Journal of Applied Physiology. 
A significant portion of the research has dealt with the use of IHT for athletic training and conditioning, one studied training approach being the so called “living high—training low” approach. This approach involves having an athlete “live” in a hypoxic environment and undergo physical training in a normoxic environment. In multiple cited studies, this approach seems to have produced measurable improvement in athletic performance and, in some studies, measurable changes in physiological and biochemical/hematological parameters. While multiple authors state that more controlled research is needed to determine the total scope and value of the applicability of this type of training for athletes, the literature supports the basic idea as valid and useful.
From an athletic perspective, individuals who are trained under hypoxic conditions are expected to develop significantly improved physical endurance responses. These improved physical endurance responses are said to include both greater physical endurance at normal (low) altitudes (below 1800 meters above sea level), in such activities as distance running and swimming, and improved endurance at high altitudes (above 1800 meters) in such activities as mountain climbing.
Research is reported to have shown, for example, that hypoxic training resulting in acclimatization to a low oxygen environment can lead not only to increased endurance in that environment, but also lead to increased physiological and biochemical adaptation and defense mechanisms, including perhaps increased erythropoetin production (with possible increase in red blood cell production); improved immune system function; adrenal stimulation; cardiovascular adaptation (e.g., reduced peripheral resistance, increased vasodilation, and increased capillary density); decreased mean arterial blood pressure and decreased heart rate; and respiratory adaptation (e.g., increased pulmonary capacity, increased hypoxic ventilatory response, increased total lung capacity, increased vital lung capacity, and increased minute ventilation).
Controlled studies appear to have shown that athletes who have naturally occurring or congenital blunted ventilatory drives (i.e., less sensitivity and natural response to increased carbon dioxide and decreased oxygen levels in the blood) experience less dyspnea (i.e., subjective difficulty or distress in breathing or shortness of breath) and lower work of breathing at given levels of work, which may make exercise and athletic performance both more comfortable and more efficient. Such a blunted ventilatory drive may be one factor which predisposes certain individuals to outstanding athletic performance. It is postulated in the art that the equivalent of a natural blunted ventilatory drive can be achieved through physical training in a hypoxic environment, including the resulting benefits to endurance, athletic performance, and comfort and efficiency of exercise and athletic performance.
Studies also are reported to have shown that the changes produced by physical training in a hypoxic environment will decrease, even with continued physical training, in a normal-oxygen environment. The implication is that sustained hypoxic training is necessary to retain the benefits of hypoxic training.
While there apparently are significantly fewer references regarding therapeutic uses of IHT, several abstracts located cover the therapeutic uses of IHT, including the use of IHT to treat lesions of the gastroduodenal mucosa (ulcers) and the use of IHT to prevent refractory hypoxemia during chest surgery. Although we have no direct evidence to support any such benefits, it has also been said that hypoxic training may possibly provide increased resistance to ionizing radiation; improved resistance to poisons and venoms; improved resistance to viral infections; decreased recovery time after surgery; increased (improved) exercise till exhaustion (ETE) time; protection of the brain from oxidative stress; increased positive benefits from adaptive sleep; and improvements in a number of classes of diseases (e.g., ischemic heart disease, hypertension, bronchitis and asthma, gastric and duodenal ulcer disease, liver and pancreatic disease including diabetes, motor diseases and gynecological diseases.
In summary, studies known in the art appear to have established that physical training in a hypoxic (lower-than-normal oxygen concentration) environment can produce beneficial changes in biochemical and physiological functioning of the body, can produce beneficial improvement in and resistance to certain disease processes, and can produce beneficial improvement in athletic performance and endurance.
The many potential benefits of, and the wide range of potential uses and applications of, hypoxic environment physical training point to the value of developing hypoxic environment training methods and devices which are practical, cost effective, portable, and flexible.
The oldest and most direct method of hypoxic environment training is to have individuals or teams train at high altitudes, e.g., 1500 meters and higher. The cost, inconvenience, and danger from the environment, along with the lack of flexibility for the “high-low” approach (other than by moving up and/or down a mountain) make this an impractical method of hypoxic environment training in most cases. More accepted methods of hypoxic environment training now include sealed chambers or tents, and breathing masks used with pressurized tanks of low concentration oxygen or with pressure swing adsorption apparatus to produce a hypoxic gas. These methods allow flexibility in the composition of the breathing gasses delivered to trainees (adjusting the composition with more nitrogen and less oxygen for more hypoxic conditions) based primarily on the time that the user is in the hypoxic environment or breathes the hypoxic gas.
The isolation chamber and the tent both have the drawback of lack of mobility; the user must be stationary, within the sealed chamber or tent, and must travel to the location of the chamber or tent for each hypoxic training session. On the other hand, the use of a face mask, to which a regulated flow of hypoxic breathing gas is delivered, provides the user with some mobility during use, but still requires that the user be relatively stationary because of the relative size of the equipment. This forms the basis for the “high-low” approach to intermittent hypoxic training by exposure to hypoxic treatment for fixed periods of time, e.g., every 30 minutes for a prescribed amount of time within a predetermined training regimen. Thus, more vigorous motion or required exercise necessarily must stop or be significantly curtailed while the user is inhaling the hypoxic gases.